fs_mgr: trigger dm-verity error handling for invalid signatures

Currently, the device doesn't mount verified partitions if the
verity table signature is invalid, which usually means it fails to
boot. This change instead sets up dm-verity with an invalid root
hash and triggers device-specific error handling to recover from
the corruption.

Bug: 24256506
Change-Id: I6d693306fa0e7459c5500b028e433df61ecea6fb
(cherry picked from commit 47caa5c3)